Commit a8af7246 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
Browse files

sched: Avoid division by zero 



Patch a5004278 (sched: Fix
cgroup smp fairness) introduced the possibility of a
divide-by-zero because load-balancing is not synchronized
between sched_domains.

This can cause the state of cpus to change between the first
and second loop over the sched domain in tg_shares_up().

Reported-by: default avatarYinghai Lu <yinghai@kernel.org>
Signed-off-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Jes Sorensen <jes@sgi.com>
Cc: Jens Axboe <jens.axboe@oracle.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
LKML-Reference: <1250855934.7538.30.camel@twins>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent cde7e5ca

kernel/sched.c

+10 −13
Original line number Diff line number Diff line
@@ -1522,7 +1522,8 @@ static void __set_se_shares(struct sched_entity *se, unsigned long shares); 
 */

static void

update_group_shares_cpu(struct task_group *tg, int cpu,

			unsigned long sd_shares, unsigned long sd_rq_weight)

			unsigned long sd_shares, unsigned long sd_rq_weight,

			unsigned long sd_eff_weight)

{

	unsigned long rq_weight;

	unsigned long shares;
@@ -1535,13 +1536,15 @@ update_group_shares_cpu(struct task_group *tg, int cpu, 
	if (!rq_weight) {

		boost = 1;

		rq_weight = NICE_0_LOAD;

		if (sd_rq_weight == sd_eff_weight)

			sd_eff_weight += NICE_0_LOAD;

		sd_rq_weight = sd_eff_weight;

	}



	/*

	 *           \Sum shares * rq_weight

	 * shares =  -----------------------

	 *               \Sum rq_weight

	 *

	 *             \Sum_j shares_j * rq_weight_i

	 * shares_i =  -----------------------------

	 *                  \Sum_j rq_weight_j

	 */

	shares = (sd_shares * rq_weight) / sd_rq_weight;

	shares = clamp_t(unsigned long, shares, MIN_SHARES, MAX_SHARES);
@@ -1593,14 +1596,8 @@ static int tg_shares_up(struct task_group *tg, void *data) 
	if (!sd->parent || !(sd->parent->flags & SD_LOAD_BALANCE))

		shares = tg->shares;



	for_each_cpu(i, sched_domain_span(sd)) {

		unsigned long sd_rq_weight = rq_weight;



		if (!tg->cfs_rq[i]->rq_weight)

			sd_rq_weight = eff_weight;



		update_group_shares_cpu(tg, i, shares, sd_rq_weight);

	}

	for_each_cpu(i, sched_domain_span(sd))

		update_group_shares_cpu(tg, i, shares, rq_weight, eff_weight);



	return 0;

}

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